Analysis of Factors Influencing the Performance of a Zero Head Hydro Energy Harvester

Transcription

1 RESEARCH PROPOSAL FOR: Analysis of Factors Influencing the Performance of a Zero Head Hydro Energy Harvester SUBMITTED TO: FACULTY OF ENGINEERING, THE BUILT ENVIRONMENT AND INFORMATION TECHNOLOGY OF THE NELSON MANDELA METROPOLITAN UNIVERSITY FOR THE PROPOSED RESEARCH PROGRAMME: Magister Technologiae: Engineering: Mechanical BY: Adriaan Jacobus Opperman Student Number: Submitted: Supervisor : Dr Russell Phillips Co-supervisor : Prof. Danie Hattingh

2 1. Introduction Since antiquity nature provided mankind with flowing water and one such example is rivers. This flow of water is driven by a difference in height from the start of the river to the end. This difference is also known as the head. Due to the fact that the water is moving it has kinetic energy. The concept of harnessing this hydrokinetic energy has been around for many years. A number of devices exist that extract energy from flowing water. Most of these devices utilize a differential water level (head). A well-known example of this is the hydraulic ram (1). Extraction of hydrokinetic energy from flowing bodies of water where no differential in level exists is also possible (2) however few successful installations are currently in use in South Africa. 2. Objective This research is to develop a Zero Head Hydro (ZHH) energy harvester with a increased efficiency to conventional machines in use. 3. Problem Statement Factors contributing to the performance of ZHH are not well documented. The main variable needs to be identified and evaluated to determine optimum design and installation conditions. 4. Sub Problems 4.1. Design of a working model that will be used for evaluation and optimisation Development of optimum shape of paddles or blades evaluates, compare and document performance The influence of augmentation devices to increase flow velocity Safety mechanism in case of flooding dealing with debris and high water levels. 1

3 5. Hypothesis This research will identify critical variables for the ZHH platform optimisation which will allow for increased efficiency. The main contributing factors would be design optimisation and flow convergence. 6. Delimitation of the research 6.1. Three types of ZHH machines will be analysed Axial flow underwater type Cross flow underwater type Paddle wheel type Experiments will be only conducted in a 700mm wide controlled open channel ZHH experimental platform with a max power output of less than 1kW will be considered. 7. Significance of Research: 7.1. For agriculture and rural communities in South Africa If energy can be extracted from flowing water such as rivers, it can be utilized for pumping water or generating electricity. The availability of this cheap renewable energy in areas without grid electricity will enhance agriculture as well as the quality of life in rural communities and small farmers For NMMU This project will enhance the NMMU s focus on sustainable renewable energy research and broaden the knowledge base in this field. 8. Preliminary Literature Review 8.1. Axial flow underwater turbine An axial flow underwater turbine can be described as a turbine with the rotational axis parallel to the incoming water stream utilizing lift or drag type 2

4 blades (3). An example of an inclined axis Garman axial flow water current turbine is shown in Figure 1. Figure 1: Inclined Garman Turbine (4) This particular configuration was installed by a company called Action Contre la Faim (ACF) in the Nile near Juba a major Southern Sudan city. The purpose of the installation was to supply drinking water to the local population. A Gamin under water turbine can produce blade efficiencies of up to 30% and power output of up to 3kW with a constant hydrofoil rotor blade and pitch. To connect the rotor to the centrifugal pump a two stage belt drive was used. This allowed the rotor to operate as close as possible to the most efficient tip speed ratio over a wide range of water speeds (4). The performance range is as follows. 1. The minimum viable river current speed is 0.6 m/s in which a turbine with a 4m diameter rotor will deliver 2 l/s of water to a 4m static head or 100 W of electricity from a 240 V generator. 3

5 Power (W) 2. At 1.2 m/s a 3.4 m rotor diameter machine would give an electrical output of 820 W. 3. At 1.9 m/s the corresponding figures are 2.2 m diameter and 1750 W. Above 2.0 m/s the rotor diameter would be sized to limit the system output to about 2 kw. To illustrate the figures above look at Graph 1. This graph compares the actual power produced to the Bets limited power to the available kinetic power from the flowing water. Power Comparison Actual Power Output (W) Ideal Power Output (W) Kinetic Power Output (W) Graph 1 The kinetic power available from flowing water is given by (5): Were: To calculate the power output from a rotor device such as the Garman the following formula is used (5): Were: 4

6 According to Dixon (5) under ideal theoretical conditions the maximum value of is Therefore only 59.3% of the available kinetic power can be used as output power under ideal conditions. This limitation is called the Betz limit. Most well designed machines will have a of between 0.3 and The maximum pumping head is 25 m using a single turbine, but by installing turbines side-by-side with their pumps in series, higher heads can be generated. For electricity generation at 240 V, a three-phase induction motor is used as a generator with an electronic controller and ballast load. For battery charging, a permanent magnet alternator is used. On a 240 V system operating in northern Sudan, both generator and pump are fitted to the machine, allowing the farmer to pump during the day and have electricity at night (4). Figure 2: River current turbine on the Nile, Sudan, 1982 (8) 5

7 According to Khan (2), within a period of four years, a total of nine of these Garman prototypes were built and tested in Juba, Sudan on the White Nile totalling 15,500 running hours. Figure 3: Axial flow water turbines: (a) inclined axis, (b) float mooring; (c) rigid mooring (2). Figure 3 illiterates three installation possibilities to utilize the axial flow underwater turbine configuration Cross flow underwater turbine Cross flow underwater turbines can be horizontal or vertically orientated and differs from the axial flow underwater turbine by having the rotational axis perpendicular to the flowing stream of water (6). An advantage of the cross 6

8 flow under water turbine is that most of them rotate unidirectional even with bidirectional fluid flow (7). As mentioned above the cross flow turbines can be divided into two groups, vertical and horizontal. In the vertical axis domain the use of H-Darrieus or Squirrel Cage Darrieus is rather commonly used for power generation from wind but nearly non-existent in hydropower production. The Gorlov turbine is another member of the vertical axis family were the blades are of helical structure. Savonious turbines are semi drag type devices that may consist of straight or skewed blades. Some disadvantages of the vertical axis turbines are: low starting torque, torque ripple and lower efficiency. These turbines may not be self-starting therefore an external starting mechanism may be needed (7). Shown in Figure 4 are different vertical types cross flow underwater turbines. Figure 4: (a) Darrieus, (b) H-Darrieus, (c) Savonious, (d) Gorlov (2) 7

9 Furthermore the horizontal cross flow turbines are mainly drag based devices and said to be less efficient than their lift based counterparts. The large amount of material usage can be another problem for such turbines. Axial flow turbines are self-starting and the issue of start-up is not significant. However, they come with a price of higher system cost owing to the use of submerged generator or gearing equipment. Vertical axis turbines, especially the H-Darrieus types with two or three blades are reasonably efficient and simpler in design, but not self-starting. Mechanisms for starting these rotors from a stalled state could be devised from mechanical or electromechanical perspectives (7). Figure 5: Atlantisstrom turbine (6) Shown in Figure 5 is the Atlantisstrom horizontal cross flow turbine designed and tested by Braunschweig Technical University, Harzwasserwerke GmbH and Volkswagen - Coaching GmbH in Bad Harzburg, Germany (6) Paddle wheel type The vertical paddle wheel can also be seen as a cross flow device since the axis of rotational is perpendicular to the direction of flow. However the paddle wheel is not submerged. According to Denny the maximum efficiencies of the conventional overshot and undershot paddlewheels are 63% and 22% respectively (8). 8

10 Figure 6: (a) Overshot Paddlewheel, (b) Undershot Paddlewheel (7) Denny (8) goes on and explains why the undershot paddle wheel is still used even though the efficiency is almost three times less than its overshot sibling. To understand this, one must appreciate the importance of waterwheels in Europe, at the beginning of the industrial revolution, prior to the widespread availability of steam engines. The Domesday Book of 1086 recorded over 5000 mills in England. By 1820 France alone had waterwheels. The dense population of mills along early 19th century European rivers and streams meant few hydro sites, so water head (height difference, and thus potential energy) became a scarce and valuable resource. Overshot wheels required a large head (2 10 m) and so were usually confined to hilly areas, or required extensive and expensive auxiliary construction, such as mill races (water flumes or sluices) that ran for hundreds of metres. Undershot wheels, on the other hand, could operate with less than 2 m head and so could be located on small streams in flat areas, nears to population centres. Due to the lack of head the undershot paddle wheel was used near Kakamas in the Northern Cape, South Africa to pump water and is shown in Figure 7&8. 9

11 Figure 7: Undershot Paddlewheel near Kakamas Figure 8: Undershot Paddlewheel near Kakamas 10

12 9. Research Methodology 9.1. Research on current ZHH devices Comprehensive literature study A solid model of the proposed research platform will be drawn up CFD analysis of flow augmentation Construction of model for testing Systematic modification and enhancements to model to optimize efficiency If desired performance is obtained with model a full scale prototype will be built and tested in a river. 10. Budget (Estimates) Manufacturing scale model R Testing scale model R Testing platform (Manufacturing & Equipment) R Manufacturing full scale model R Testing model (Transport & Modifications) R Travelling R Printing, binding and other consumables R Total Budget R Project Timeline 12. The Researchers Qualifications National Diploma Mechanical Engineering, Nelson Mandela Metropolitan University, 2009 Baccalaureus Technologiae Mechanical Engineering, Nelson Mandela Metropolitan University,

13 Bibliography 1. HowStuffWorks.com. [Online].; 2000 [cited Available from: 2. Khan MJ, Iqbal MT, Quaicoe JE. River current energy conversion systems: Progress, prospects and challenges. Renewable and Sustainable Energy Reviews. 2008; 12(8): p Khan MJ, Bhuyan G, Iqbal MT, Quaicoe JE. Hydrokinetic energy conversion systems and assessment of horizontal and vertical axis turbines for river and tidal applications: A technology status review. Applied Energy. 2009; 86(10): p Water Current Turbines Pump Drinking Water. Technical. Oxfordshire: CADDET Centre for Renewable Energy. 5. Dixon SL. Fluid Mechanics and Thermodynamics of Turbomachinery. 5th ed. Stein J, editor. Oxford: Elsevier; Atlantisstrom. [Online].; 2004 [cited 2011 June. Available from: 7. Sornes K. Small-scale Water Current Turbines. Oslo: Zero Emissions Resource Organisation (ZERO); Denny M. The efficiency of overshot and undershot waterwheels. European Journal of Physics. 2004; 25(2): p Ainsworth D, Thake J. FINAL REPORT ON PRELIMINARY WORKS ASSOCIATED WITH 1MW TIDAL TURBINE. Marine Current Turbines Ltd;